The present invention relates to rotary fluid pressure devices, and more particularly, to such devices of the type including an integral brake assembly, suitable for braking motion either into, or out of, a rotary fluid displacement mechanism. The present invention also relates to an improved method of setting the load holding torque capability of a brake assembly associated with a hydraulic motor.
Although the present invention may be utilized in rotary fluid pressure devices in which the rotary fluid displacement mechanism comprises any one of a number of different types of mechanisms, it is especially advantageous when utilized in a device in which the displacement mechanism comprises a gerotor gear set, and will be described in connection therewith. As used herein and in the appended claims, the term xe2x80x9cgerotorxe2x80x9d will be understood to mean and include both a conventional gerotor device, in which the ring member includes integrally-formed internal teeth, and roller gerotors, in which the internal teeth of the ring member comprise cylindrical roller members.
Furthermore, the present invention is especially suited for use in a gerotor-type device which comprises a low-speed, high-torque (xe2x80x9cLSHTxe2x80x9d) gerotor type hydraulic motor, and will be described in connection therewith.
In many vehicle applications for LSHT gerotor motors, it is desirable for the motor to have some sort of parking brake or parking lock, the term xe2x80x9clockxe2x80x9d being preferred in some instances because the vehicle manufacturer intends that the parking lock be engaged only after the vehicle is stopped. In other words, such parking lock devices are not intended to be dynamic brakes, which would be engaged while the vehicle is moving, to bring the vehicle to a stop. However, the term xe2x80x9cbrakexe2x80x9d will generally be used hereinafter to mean and include both brakes and locks, the term xe2x80x9cbrakexe2x80x9d being somewhat preferred to distinguish the device of the present invention from a device which would operate in only a fully engaged or fully disengaged condition.
Recently, the assignee of the present invention has developed, and has begun to commercialize a gerotor motor including an integral brake package which, for many vehicle applications, is quite satisfactory in performance, is fairly simple and inexpensive, and is quite compact. The gerotor motor and brake package referenced above is illustrated and described in U.S. Pat. No. 6,132,194, assigned to the assignee of the present invention and incorporated herein by reference.
Typically, brake packages which are used with hydraulic motors, and especially those brake packages used as integral brake packages with LSHT gerotor motors, are of the xe2x80x9cspring-applied, pressure-releasedxe2x80x9d type as is now well known to those skilled in the art. In other words, the braking members (e.g., friction discs, etc.) are biased toward braking engagement by some sort of spring arrangement, and are move toward a brake-disengaged condition by hydraulic pressure. As is now well known to those skilled in the art, the hydraulic pressure to disengage the brake may be internal case pressure, or an external xe2x80x9cpilotxe2x80x9d pressure from a system charge pump, or any other suitable source of pressure, the details of which are not essential features of the present invention.
As is also well known to those skilled in the art, one of the primary performance criteria of a brake package of the type to which the present invention relates is the xe2x80x9cload holding capacityxe2x80x9d of the brake assembly. In a typical spring-applied, pressure-released brake assembly, the load holding capacity (or load holding torque) is a direct function of the springs which bias the brake assembly into braking engagement.
Therefore, although the brake assembly of the above-incorporated patent operates in a very satisfactory manner, the increasing commercial popularity has uncovered one shortcoming of the design. As the motor and brake assembly are used on a greater range of vehicle applications, the assignee of the present invention has been requested to provide motor and brake assemblies having a wide range of load holding torques. Unfortunately, providing one basic motor and brake assembly which has a different load holding torque for each of several different customers and vehicle applications requires the motor manufacturer to, for example, provide a different endcap (having a different length of brake chamber) for each load holding torque desired. However, as is well known to those skilled in the art, a proliferation of part numbers for the same basic motor component adds substantially to the overall cost of manufacture of the motors.
Alternatively, for each desired load holding torque, a different sized spring shim member can be utilized (i.e., having a different axial length) to provide a different spring preload on the axially moveable member of the braking package. However, the need to specify and stock a different shim for every possible load holding torque which may be desired also adds substantially to the overall complexity of the assembly process and the cost of manufacture of the motor.
Accordingly, it is an object of the present invention to provide an improved rotary fluid pressure device and brake assembly which overcomes the above-described disadvantages of the prior art brake assembly.
It is a more specific object of the present invention to provide a gerotor motor and brake assembly for use therein which can be integral with the motor, but can provide any desired one of a wide range of load holding capacities, without the need for selection among a large number of various sizes of a common component.
It is a further object of the present invention to provide a gerotor motor and brake assembly which accomplishes the above-stated objects, and which increases the likelihood that each motor, when it is made and assembled, will provide the load holding capability desired by the customer for that particular motor, without any further changes or adjustments, either in the motor assembly plant, or at the customer""s vehicle assembly plant.
It is a related object of the present invention to provide an improved method for setting the load holding torque capability of a brake assembly of a hydraulic motor, wherein the improved method does not require the use of components which are peculiar to each of the possible, desired load holding torques.
The above and other objects of the invention are accomplished by the provision of a rotary fluid pressure device of the type including a housing defining a fluid inlet and a fluid outlet. A rotary fluid displacement mechanism includes an output member having either orbital or rotational movement, the mechanism including a brake portion extending axially rearward from the output member, and operably associated with the output member such that braking movement of the brake portion results in braking of the output member. The housing defines a generally cylindrical brake chamber and a piston member is disposed in the brake chamber, the piston member being moveable between a first, retracted position under the influence of fluid pressure in the brake chamber and a second, engaged position under the influence of a biasing spring disposed in engagement with a rearward side of the piston member.
The improved rotary fluid pressure device is characterized by the housing defining a set of internal threads disposed adjacent the piston member. An enclosure member has a forward surface comprising a spring seat for the biasing spring. The enclosure member defines a set of external threads in threaded engagement with the set of internal threads, whereby the axial location of the enclosure member and the spring seat is adjustable in response to rotation of the enclosure member, to vary the load holding torque of the brake portion.
In accordance with a more limited aspect of the invention, the improved rotary fluid pressure device is characterized by the biasing spring exerting an axial force in a rearward direction on the enclosure member, the axial force comprising substantially the only means for retaining the enclosure member within the set of internal threads defined by the housing.
In accordance with another aspect of the present invention, there is provided an improved method for setting the load holding torque of a brake package operably associated with a hydraulic motor. The motor is of the type comprising a housing defining a fluid inlet and a rotary fluid displacement mechanism including an output member and an output shaft and means for transmitting torque from the output member to the output shaft. The brake package is of the spring-applied type and includes a brake portion operably associated with the output member, and a piston member moveable between a first retracted position, and a second, engaged position under the influence of a biasing spring. A member is disposed adjacent the piston member and has a forward surface comprising a spring seat for the biasing spring.
The improved method is characterized by:
(a) applying to the output shaft a resistance load corresponding to a desired load holding torque, the resistance load causing rotation of the output shaft when the piston member is in the first, retracted position; and
(b) moving the member axially in a direction tending to increase the bias preload on the biasing spring until the output shaft no longer rotates.